The carboxylic esters of γ-hydroxy tiglic aldehydes have attracted strong industrial interest, as they are known intermediates for vitamin-A and various perfumistic products. Various methods have been described in the prior art for the preparation of these esters. U.S. Pat. No. 3,760,004 by Freyschlag et al, discloses the preparation of these esters by halogenating a member of the group consisting of 2-formyl-2-hydroxybutene-3 and a di-lower alkyl acetal and a lower fatty acid acylate, with a halogenating agent selected from the group consisting of thionyl chloride, thionyl bromide and phosgene in the presence of a tertiary amine. This conventional process for the synthesis of the carboxylic esters of γ-hydroxy tiglic aldehyde suffers from the drawback of using harmful gases like phosgene, thionyl chloride or thionyl bromide. Bis-monocarboxylicacid esters of 3-formylbutane-1,2-diol have also been used as starting materials for the synthesis of the esters of γ-hydroxy tiglic aldehydes as disclosed in U.S. Pat. No. 3,732,287 by Himmmele et al. This patent describes a process where Bis-monocarboxylicacid esters of 3-formylbutanediol-1,2 are hydroformylated in the presence of carbonyl complex of rhodium at elevated temperatures and super atmospheric pressures. The pressure requirements are from 300-1000 atmospheres. The use of very high temperatures and pressures involves the use of expensive equipment and costly handling procedures to get the desired product. The use of such high pressures mitigates against the commercialization of this process. U.S. Pat. No. 4,124,619 by Fitton et al, discloses another method of synthesis, via the hydroformylation route, using biscarboxylic acid esters of but-2-ene-1,4-diols as the starting material to give carboxylic esters of γ-hydroxy tiglic aldehydes. In this patent biscarboxylic acid esters of but-2-ene-1,4-diols are converted to the compound of the formula 2 by treating with a mixture of carbon monoxide and hydrogen in the presence of a Rhodium catalyst. In a separate step the compound 2 is converted to compound 3 by pyrolysis in the presence of a strong organic or inorganic acid catalyst at a temperature of from 70° C. to 250° C. at atmospheric pressure or under vaccum of 1 mm Hg to 700 mm Hg. This patent describes the hydroformylation route using the homogeneous Rhodium catalyst system. The major disadvantage of this route is a great difficulty in separating the catalyst from the reaction mixture. Distillation has to be done to separate the products from the catalyst system. The catalyst is not stable after distillation at higher temperatures. And then deacetoxylation is done as a separate step, which requires the presence of strong acid catalysts or elevated temperatures.
The conventional processes for the synthesis of carboxylic esters of γ-hydroxy tiglic aldehydes suffer from many drawbacks. The earliest procedures by conventional routes require the use of harmful halogenating gases (U.S. Pat. No. 3,760,004). The later processes using the oxo reaction proved to be non-economical because of the very high-pressure requirements (U.S. Pat. No. 3,732,287). Another process using the hydroformylation route at comparatively lower pressure conditions uses the Rhodium catalyst system in the homogeneous reaction conditions, and so there is a difficulty in separating the catalyst from the reaction mixture and there is a loss in the amount of product upon distillation (U.S. Pat. No. 4,124,619). And deacetoxylation to get the required carboxylic esters of γ-hydroxy tiglic aldehydes is a two-step process.
There is a commercial interest in carboxylic esters of γ-hydroxy tiglic aldehydes, as they are well known intermediates for vitamin-A and various perfumery applications. An increasing academic as well as industrial attention has been paid towards research in developing new methods for the higher selectivity of carboxylic esters of γ-hydroxy tiglic aldehydes and easy catalyst separation from the reaction mixture. In view of the advantages and the features of the present invention, this improved process, would be a significant advance in the current state of art related to the synthesis of carboxylic esters of γ-hydroxy tiglic aldehydes by the hydroformylation route, having easy catalyst separation and a 100% selectivity towards carboxylic esters of γ-hydroxy tiglic aldehydes in a single step.